1. Field of the Invention
The invention is directed to optical communication systems in general and, more particularly, to optical networks that include two or more waveguides each transporting a WDM optical signal composed of plural optical channels and having a data bridge for directing selected bit streams encoded on one optical channel from one waveguide to plural channels carried in a WDM optical signal on another waveguide.
2. Description of the Related Art
As the need for communication signal bandwidth increases, wavelength division multiplexing (WDM) has progressively gained popularity for multiplying the transmission capacity of a single optical fiber. A review of optical networks, including WDM networks, can be found in Ramaswami et al., Optical Networks: A Practical Perspective (Morgan Kaufmnan,(copyright) 1998), the disclosure of which is incorporated herein by reference. Typically, wavelength division multiplexed optical communication systems have been designed and deployed in the long-haul, interexchange carrier realm. In these long-haul optical systems, a wavelength division multiplexed optical communication signal comprising plural optical channels at different wavelengths travels in a single direction on a single fiber. Because the communication traffic in such systems commonly travels many hundreds of kilometers, the need for add-drop multiplexing of individual channels is infrequent (if at all), occurring at widely-spaced add-drop nodes.
Although the optical infrastructure of long-haul WDM optical systems can accommodate future traffic needs created by increased demand from traditional and multimedia Internet services, this traffic must first be collected and distributed by local networks. Currently, such local networks are predominantly structured to carry a single wavelength, time-division multiplexed (TDM) optical signal along a fiber network organized into various ring structures. To route the various components of the TDM signal, numerous electronic add-drop multiplexers are positioned along the fiber network. At each add-drop location, the entire optical signal is converted into an electrical signal; the portions of the electrical signal which are destined for that add-drop point are routed accordingly. The remaining portions of the electrical signal are converted back to a new TDM optical signal and are output through the electronic add-drop multiplexer. Thus, before a user can access the bandwidth-rich WDM long-haul transport networks, he must first pass through the bottleneck of the local networks.
Although WDM optical systems are suitable for conventional long-haul interexchange carrier markets, metropolitan (local) communications systems require extensive routing and switching of traffic among various nodes positioned within interconnecting optical fiber rings. Consequently, smaller metropolitan markets require considerably more extensive add-drop multiplexing in order to successfully implement wavelength division multiplexing in their short-range systems. In addition to the difficulties posed by frequent add-drop multiplexing channels it would be desirable to direct channels from one DM optical waveguide to another. For example, in a local metropolitan network, it would be desirable to transfer traffic among adjacent rings. Further, it would be desirable to route different portions of a single optical channel carried by one waveguide to plural channels carried on another waveguide. Such a device would permit effective implementation of wavelength division multiplexing in local, metropolitan markets requiring high volumes of signal re-routing and allow creation of flexible network topologies.
The present invention relates to an optical network including a bridge for selectively transferring information from an optical channel which forms part of a first WDM optical signal carried on a first waveguide to at least two optical channels which forms part of a second WDM signal carried on a second optical waveguide. A bridge is interposed between the first and second optical waveguides. The bridge includes a first optical add-drop multiplexer optically communicating with the first waveguide which selects at least one optical channel from the first WDM signal. The first optical channel carries a first series of data bits and a second series of data bits encoded on the optical channel.
The bridge also includes a first optical network interface which includes an optical to electrical conversion element for converting the selected first optical channel to at least two electrical signals which respectively include the first and second series of data bits. The plural electrical signals may be directly created from the optical signal or they may be derived from an electrical signal which includes both the first and second series of data bits which is subsequently separated into plural electrical signals.
The electrical signals respectively encoded with the first and second series of data bits electrically communicate with a second optical network interface. The second optical network interface includes at least two electrical to optical conversion elements such that the second electrical signal encoded with the first series of data bits is used to modulate a second optical channel and the third electrical signal encoded with the second series of data bits is used to modulate a third optical channel. These optical channels are sent to a second optical add-drop multiplexer optically communicating with the second optical waveguide where they are added to the WDM optical signal propagating on the second waveguide.